Explosive devices are normally designed to be activated by means of a chain of explosions in which, initiation/ignition of a small quantity of sensitive explosive material, ignites a larger quantity of more powerful and less sensitive material. This in turn ignites a larger quantity of more powerful and less sensitive material, and so forth up the chain until the main explosive charge is ignited. The main reason for the explosive chain is safety, since removal of any one of the links in the chain prevents the ignition of the link above it.
Depending on the type of energetic material that is inside of it the first element in the chain is known by many different names, e.g. igniter, detonator, initiator, and squib. Herein the generic term “energetic unit” will be used to refer to any or all of this type of element that is used in applications including but not limited to: initiating an exploding train in “Safe and Arm” systems, mines, and other exploding application; initiating thermal batteries by activating there thermo-electric layers; and ignition of rocket motors. Energetic units can take many forms from a simple match to sophisticated semiconductor devices.
A type of igniter that is commonly used today in military applications is known as a “hot wire igniter”. Such igniters are well known and documented in the prior art. They are composed of a segment of electric wire connected in series to two electrodes. The segment of wire is in thermal contact with a quantity of very sensitive energetic material. Passing an electric current through the wire causes its temperature to rise until the heat generated in the wire is sufficient to ignite the energetic material. In some embodiments of hot wire igniter the hot wire is connected between an electrode and a metal casing that functions as one of the electrodes. Related types of igniter are “exploding wire igniters” and “exploding foil igniters” in which a high voltage is applied causing the wire to melt and a shock wave that ignites the energetic material.
The structure of the hot wire igniter—specifically the requirement of a minimal length to the hot wire, the diameters of the electrode wire and surrounding electrical insulation, and the energy requirements—limits the ability to design miniaturized systems that depend on these igniters for activation. Examples of applications of such miniaturized systems are very small thermal batteries for use in a variety of applications and small diameter munitions.
Since many applications that employ thermal batteries are located in environments, e.g. rockets and missiles, in which both space and energy are in very short supply there is an increasing interest on developing new types of energetic unit that provide a response to the design challenges of reducing both size and energy requirement.
One promising approach has been the development of devices produced using semiconductor technology. A semiconductor bridge technology has been described in the literature and a few patent documents, e.g. U.S. Pat. No. 4,708,060, U.S. Pat. No. 4,819,560, and U.S. Pat. No. 5,861,570. In these devices a segment of doped or undoped semiconductor matter acts as a bridge between two 30 conducting lands. When an electrical potential is applied to the lands an electric current flows through the bridge creating a plasma which ignites an energetic material that is in contact with or in close proximity to the bridge. To the best of the knowledge of the inventor no commercial use, at least not in military applications, has been made of this technology.
It is a purpose of the present invention to provide a miniaturized energetic unit that can be used in a variety of applications.
It is another purpose of the present invention to provide a miniaturized energetic unit that is activated by a very small quantity of energy.
It is another purpose of the present invention to provide a miniaturized energetic unit that is manufactured using techniques of MEMS technology, thereby allowing not only extreme miniaturization but also low expense.
Further purposes and advantages of this invention will appear as the description proceeds.